I am having thethe same problem on Samsung. It's only happening with pictures and usually with one specific contact. She always gets the pictures, but days later I will get an unspent message notification.
Hello. What is the ZIP Code for your location, so I may review your area for any open alerts? TaylorH_VZW
Kittytastrophy, alarming messages would certainly have me wondering what was happening. When did you first notice this message? When checking your messages do any appear to have an exclamation point next to them? Do you use Wi-Fi regularly? Which make and model phone are you using? LorenB_VZW If my response answered your question please click the _Correct Answer_ button under my response. This ensures others can benefit from our conversation. Thanks in advance for your help with this!!
I can't recall exactly when it first started. But I know it's been going on for quite a while now. Yes messages have an exclamation mark next to them. I have the Samsung Galaxy S8, and use Wi-Fi when is available.
Thank you, Kittytastrophy. Do you notice a change in how the messages are marked if Wi-Fi is turned off?